Computer assisted intervention (CAI) systems require the integration of an increasing number of devices, including medical monitors, sensors, tracking devices and robots. This complexity makes applications harder to develop, more difficult to debug and the accumulation of ad hoc interfaces reduces the overall portability. We describe a set of libraries, the cisst libraries, developed at the Johns Hopkins University to address some of the problems encountered when integrating devices for CAI. We focus on three main characteristics of the cisst libraries: software architecture, multi-threading and CAI specific interfaces.